The present invention relates to syringe assemblies and more particularly concerns syringe assemblies for use in I.V. flush procedures.
An I.V. catheter is a commonly used therapeutic device. Many patients, in accordance with their therapy, have an I.V. catheter connected to a vein ready for use in various procedures or in fluid communication with an I.V. system for infusing liquids and medication. Many I.V. sets have I.V. ports which are in fluid communication with a catheter and allow access for the purpose of injecting medication into the patient, and for use in flushing techniques to maintain catheter patency and integrity. Healthcare facilities have flushing protocols which depend on the amount of time the catheter will remain in the patient and the type of catheter being used. For example, a peripherally inserted central catheter (PICC) is a long flexible catheter, which is typically inserted into the central venous system (optimally with the tip terminating in the superior vena cava) via the superficial veins of the antecubital fossa. PICC lines are designed for use when intermediate or long-term therapy is prescribed. These catheter lines must be periodically flushed with saline flush solution and/or heparin lock flush solution depending on the protocol. Among other things, flushing saline solution removes blood from the catheter and heparin helps prevent the formation of future blood clots. The most common I.V. ports are covered by pierceable septums or pre-slit septums and are known in the art and sometimes referred to as “PRN” from the Latin pro re nata meaning “as the need arises”. The septum is preferably made of rubber or another elastomeric material which permits insertion of a sharp needle cannula in order to infuse fluids into or to withdraw fluids from the catheter. Upon withdrawal of the needle cannula the septum seals itself. Ports having pre-slit septums are used with blunt cannula. Typically, the blunt cannula is attached to a syringe and the syringe is moved to place a gentle pressure on the pre-slit septum which is forced open by the blunt cannula to establish fluid communication. Also, some I.V. sets have access valves which are responsive to the frusto-conically shaped tip of a syringe barrel for allowing fluid communication between the interior of the syringe and the catheter.
Catheters are flushed using syringe assemblies filled with various fluids. In some cases, different fluids are injected sequentially in accordance with the protocol. For example, a saline solution followed by an anticoagulant such as heparin. The size of the syringe used to flush I.V. lines varies by various factors including the size and length of the catheter. Typically syringes of 1 ml, 3 ml, 5 ml and 10 ml volume are used. A commercially available 1 ml syringe may have a barrel inside diameter of approximately 6.6 mm (0.26 inch), a 3 ml syringe may have a barrel inside diameter of approximately 8.6 mm (0.34) inch while a 10 ml syringe may have a barrel inside diameter of approximately 14.5 mm (0.57 inch). Unfortunately, during the flushing of vascular access devices, different nominal size syringes generate substantially different pressures in the solution being injected by the same force being applied to the syringe plunger rod. For example, a ten-pound force on the plunger rod may cause a 10 ml syringe to generate 40 psi of liquid pressure while a 3 ml syringe generates 110 psi and a 1 ml syringe generates 190 psi.
Control of pressure is very important during flush procedures for detection of resistance to flow or catheter occlusion, and to avoid over-pressure because of the danger of dislodging a clot or rupturing the catheter. Accordingly, many practictioners are believed to prefer the 10 ml size syringe because when using the 10 ml syringe it is easier to observe possible catheter occlusion and it is less likely to provide excessive pressures which could dislodge a blood clot or damage the catheter.
Also, it is important in the flush procedure not to draw blood back into the catheter where it can clot and seal the catheter. In order to prevent blood reflux into the catheter the user is encouraged to maintain a positive pressure in the line during the flush procedure. This may involve slowly withdrawing the syringe and cannula from the I.V. port while still applying pressure to the syringe plunger rod. When using a syringe with an elastomeric stopper, if the stopper is compressed by action of the plunger rod, release of the plunger rod causes the stopper to expand and may cause blood to enter the catheter line.
Although a wide variety of catheters and I.V. ports can be adequately flushed using currently available syringe assemblies, there is still a need for simple, straight forward easy-to-manufacture syringe assemblies which eliminate the substantial pressure variations possible with the present syringes and minimize the potential for accidentally drawing blood in the catheter during the flush procedure.